Responding to the more-important-than-ever voice of the customer, automaker and supplier engineers and designers are constantly working to make auto interiors more comfortable. Features like separate temperature controls for driver and passengers and multiple-way power seats are becoming commonplace. Now attention turns to the invisible and microscopic.

Filter manufacturer Donaldson Co. Inc. and materials supplier Hoechst Celanese Corp. are introducing the Ultra Aire XL, which promises to eliminate odors as well as airborne particles in vehicle passenger compartments.

The new filter is designed to trap pollens, molds, fungi, tobacco smoke and other environmental irritants and eliminate odors such as diesel and gasoline exhaust fumes, air pollution and all but the freshest skunk evidence.

It accomplishes this feat with a combination of two advanced technologies. The first is Donaldson's Ultra-Web synthetic, non-glass, micro-fiber filter material, which is the world's thinnest - at less than one micron - says Richard Canepa, director of the company's cabin air filtration business.

The advantage of the thinner material, says Mr. Canepa, is that it traps more particulates while offering lower pressure drop. That means freer air passage through the vehicle's heating, ventilation and air conditioning (HVAC) system and less stress on blowers and fans.

The manufacturing technique that gives the fiber its fineness is so proprietary that even Mr. Canepa isn't allowed to see it.

The other notable technology is the patented Hoechst Celanese fiber technique that fully immobilizes activated carbon beads, which absorb odors. Jeanne Smith, air quality filtration market development specialist at Hoechst Celanese, says one ounce of the activated carbon is equal to seven and a half football fields of filter surface area.

Two features differentiate the new Donaldson filter from a similar product that 3M Corp. supplies for the BMW 7 series. Both utilize activated carbon to purify the air, but 3M's filter fiber measures 10 to 30 microns wide compared to Donaldson's less-than-one. The other is that the Donaldson filter is not electrostatically charged.

Mr. Canepa says most filters are charged to help them attract particulates, but adds that any contact with moisture eliminates the effect of the electric charge. He says these charged filters start out effective, lose capability when the charge wears off, and improve over time as matter builds up and helps capture more particles. Due to the size of its fiber, the Ultra Aire XL doesn't need the charge, he says.

Mr. Canepa says the Ultra Aire XL (with the activated carbon) will cost two to two and one-half times more than a standard Ultra Aire. That translates into about $50 or $60 to consumers, who will have a chance to try the new filter via the aftermarket in about six months. Within a year, Mr. Canepa expects to have an OEM platform application for introduction around the turn of the century.

"Right now, OEMS are at the particulate filter stage," says Mr. Canepa. "But I guarantee once you have this one, you'll notice when you don't have it."